Such devices, in the current state of the art, comprise on the one hand a fan capable of creating an air flow at a relatively high speed, and on the other hand sprayers provided with nozzles capable of dispersing liquid contained in a tank and passed to the nozzles by means of a pump, these nozzles being placed in said air flow. Depending on whether it is desired to treat short plants or, by contrast, relatively tall plants, different devices are used which are capable of sending the jet either upwards or downwards. In the first case, the fan is generally placed in the low part of the device, and a pipe or a duct of suitable shape rises to a height adequate to send the air jet in the appropriate direction. The nozzles for the spraying of liquid are placed at the outlet of the air guidance ducts, whether said air is sent upwards or downwards. When it is desired to treat trees or hedges of a certain height, the device for guiding the air flow to a height similar to that of the tops of the trees contains a large-volume duct which is bulky and fragile, impedes movement and, on the other hand, entails substantial headlosses, despite its dimensions. For the treatment of shorter plants, for example vines, apparatuses exist which simultaneously deliver, from a single fan, jets directed upwards onto the lower part of the plants, and jets directed downwards onto the upper part of the same plants. It is thus possible to treat several lines of plants simultaneously. In fact, the lower air flow, passing into the zone of the trunks where the foliage is less abundant, can pass through the line and carry the product as far as the subsequent row, while the upper air flow, overhanging the tops of the rows, can itself also reach the subsequent row.
However, the apparatuses obtained in this case are extremely bulky, and their folding or dismantling for transport purposes is a delicate and time-consuming operation.